I have Hyundai Verna 1.6 sx model i getting problem that rpm is not passing 3000 and had an problem in pickup i consult with showroom and private mechanic so both said that I need to change wiring of car or have to check ecm so plz suggest me what to do

My verna fluidic was having check engine light blinking stationary.. At that time RPM was not going above 3000. I scanned and erased the sensor. scan result was rail presuure low for engine speed. After araiser rpm went above 3000 and was running smoothly. Now no engine light but rpm less that 3000 after one week of running. what can be . No lag on running below 3000 rpm.

My verna fludic 1.6 sx crdi starts well, well pick up but after some time rpm does not raise above 3000, and orange check light constant appears, I got scanned the engine found air flow less, got maas air flow censor replaced still same problem , can some friend guide me what to do ?